This invention relates to a method of manufacture and method of use of hydroprocessing catalysts and in particular those catalysts that contain molybdenum and cobalt or nickel.
Hydroprocessing catalysts contain catalytic metals which are frequently one Group VI metal with one Group VIII metal. Preferred metals include molybdenum, nickel and cobalt. A problem frequently encountered with hydroprocessing catalysts that contain molybdenum is caused by formation of the molybdate ion (MoO.sub.4.sup..dbd.) which can form molybdate salts with nickel or cobalt. Relatively large crystals of nickel or cobalt molybdate then tend to form in catalysts, concentrating the catalytic metals in the crystals, and thereby reducing the intrinsic activity of the catalyst.
Co-precipitation of the support with active metals gives a very active catalyst, but this method requires washing steps that are expensive, and the metals, particularly molybdenum, may be partially washed off the catalyst. Impregnation does not produce as active a catalyst and two or more calcining steps are necessary. U.S. Pat. Nos. 4,097,413, 4,111,795, and 4,179,410 all describe a method of comulling alumina with ammonium heptamolybdate, drying the resulting mixture under conditions to decompose the ammonium heptamolybdate, adding a cobalt salt and mulling further, extruding, drying and calcining. The drawback with this procedure is its complexity.